Rivers Rivers andandStreaStreamsms

River SystemsRiver Systems

•A river or stream: any body of A river or stream: any body of water flowing downhill in a well water flowing downhill in a well defined channeldefined channel

•Drainage Drainage basinbasin

•Drainage Drainage dividedivide

•Divided into 3 Divided into 3 subsystemssubsystems– Collecting systemCollecting system– Transporting systemTransporting system– Dispersing systemDispersing system

Stream System OrderStream System Order--Tributaries decreases downstreamTributaries decreases downstream-Tributary length increases downstream-Tributary length increases downstream-Gradient decreases -Gradient decreases downstreamdownstream-Channels are wider -Channels are wider deeper downstreamdeeper downstream

CommonDrainage Patterns

Stream Flow DynamicsStream Flow Dynamics

•Factors affecting stream behaviorFactors affecting stream behavior•Discharge (Q)Discharge (Q)

•GradientGradient

•Average velocity (V)Average velocity (V)

•Channel cross-sectional area (A)Channel cross-sectional area (A)

•LoadLoad

•Base levelBase level

Stream Flow DynamicsStream Flow Dynamics

•Discharge Discharge •The volume of water flowing past The volume of water flowing past

a given point in the rivera given point in the river•Discharge will vary with time and Discharge will vary with time and

weather conditionsweather conditions•Measured in cubic meters per secondMeasured in cubic meters per second

•GradientGradient– The slope of the stream channelThe slope of the stream channel– Change in elevation divided by Change in elevation divided by

distance (m/km)distance (m/km)– Longitudinal profile is a concave Longitudinal profile is a concave

upwardupward•Steep at headwatersSteep at headwaters

•Nearly flat at discharge areaNearly flat at discharge area

•VelocityVelocity varies within the channel varies within the channel– Highest velocity is in Highest velocity is in

the center of the channelthe center of the channel– Drag slows water along Drag slows water along

the bottom, banks, and the bottom, banks, and

top (water-air interface)top (water-air interface)

•LoadLoad– Material carried along by the streamMaterial carried along by the stream

•Suspended load (fine particles) or Suspended load (fine particles) or •Bed load (coarse particles)Bed load (coarse particles)•Dissolved load (ions in solution)Dissolved load (ions in solution)

• Base LevelBase Level - level to which a - level to which a stream will erodestream will erode

Graded Stream

Stream ErosionStream Erosion

•River systems erode the land River systems erode the land surface by:surface by:– Removal of weathering productsRemoval of weathering products– Downcutting of stream channelDowncutting of stream channel– Headward erosionHeadward erosion

Downcutting of ChannelsDowncutting of Channels• Bottom of stream channel abraded by Bottom of stream channel abraded by

transported sand & graveltransported sand & gravel

Headward ErosionHeadward Erosion• Erosion rates are greatest where Erosion rates are greatest where

stream gradients are highstream gradients are high

Headward erosion of a plateau

Stream DepositionStream Deposition

– FloodplainsFloodplains– DeltasDeltas– Alluvial valleys and fansAlluvial valleys and fans

Meandering StreamsMeandering Streams

•Rivers flow in a sinuous patternRivers flow in a sinuous pattern– Turbulent flow & velocity changes Turbulent flow & velocity changes

eroded one bank, deposit on the eroded one bank, deposit on the otherother

– Erosion changes course of riverErosion changes course of river

River at Flood Stage

Floodplain

Main Channel

FloodplainsFloodplains

• FloodsFloods– Normal stage - water level below the bankNormal stage - water level below the bank– Bankfull stage - water level even with the Bankfull stage - water level even with the

bankbank– Flood stage - water level above the bankFlood stage - water level above the bank

• FloodplainsFloodplains– Areas that will be submerged when a river Areas that will be submerged when a river

is at flood stageis at flood stage

Braided StreamsBraided Streams

•Multiple channel systemMultiple channel system– Interlaced channels with islandsInterlaced channels with islands– High sediment loadHigh sediment load– Common in arid & semi-arid regionsCommon in arid & semi-arid regions

•Seasonal high flowsSeasonal high flows

– Common in front of glaciersCommon in front of glaciers•Large sediment load, fluctuating water Large sediment load, fluctuating water

flowflow

Alluvial ValleysAlluvial Valleys

•Streams fill part of their valleys Streams fill part of their valleys with sedimentwith sediment– Changes in hydrologic conditions Changes in hydrologic conditions

initiate depositioninitiate deposition– Subsequently cut through depositsSubsequently cut through deposits

•Create terracesCreate terraces

DeltasDeltas

•Formed by sudden drop in Formed by sudden drop in velocityvelocity– Stream enters ocean or lakeStream enters ocean or lake– Stream drops sediment loadStream drops sediment load– Evolve by three mechanismsEvolve by three mechanisms– Growth may be influenced by Growth may be influenced by

ocean wavesocean waves

Delta GrowthDelta Growth

• DistributariesDistributaries– Levee and in-stream deposit formationLevee and in-stream deposit formation– Channel splits into two smaller channelsChannel splits into two smaller channels

• SplaysSplays– Crevasse allow water to leave main channelCrevasse allow water to leave main channel– Water spreads out forming a splay depositWater spreads out forming a splay deposit

• AvulsionAvulsion– Shift in main course to follow steeper slopeShift in main course to follow steeper slope

Alluvial FansAlluvial Fans

•Accumulation of sediment in a dry Accumulation of sediment in a dry basinbasin– Deposition due to rapid velocity dropDeposition due to rapid velocity drop– Usually arid climateUsually arid climate– High sediment load - braided streamsHigh sediment load - braided streams– Form fan-shaped depositForm fan-shaped deposit

Alluvial fans in Death Valley